Dehydration and Rehydration Monitoring Through Ultrasound Imaging of the Inferior Vena Cava

Human hydration level is usually assessed by employing invasive methods, like blood sample analysis, or through time-consuming laboratory techniques, such as urine analysis. This study aims to determine whether changes in the inferior vena cava (IVC), assessed through ultrasound (US) imaging, can be an alternative approach for assessing the hydration level of the user. For this purpose, 29 healthy young subjects (15 females and 14 males) were enrolled in an experimental protocol designed to induce dehydration through moderate-intensity physical activity and subsequent rehydration. During the dehydration phase, US videos of the longitudinal section of the IVC were collected at approximately 10-minute intervals, for a total of five recordings. During the rehydration phase, the videos were captured every 2 minutes, with three recordings conducted. The IVC's diameter and the caval index (CI) were estimated from the US videos during both the dehydration and rehydration phases. Participants' weight was measured in each sub-phase of the dehydration stage. An amount of water equivalent to the weight loss was administered during the rehydration phase. Results show a significant decrease in the IVC's diameter from 30 minutes of activity onwards, compared to the initial diameter (p < 0.05), and a return to the baseline condition after 4 minutes of water intake (p < 0.05). No significant differences were identified in the CIs across the whole protocol. Further studies are needed to expand the available dataset and identify potential confounding factors that can impact on our approach.